Galaxy - Solar System Solar System Galaxy Solar System Explanation ::-- Sun || Solar Planet || Mercury Planet || Jupitor Planet || Venus Planet || Earth Planet || Uranus Planet || Saturn Planet || Mars Planet || Neptune Planet || Dwarf Planet || Astroids || Comet || A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias literally "milky", a reference to the Milky Way galaxy. Examples of galaxies range from dwarfs with as few as ten million (107) stars to giants with a hundred trillion (1014) stars, each orbiting their galaxy's own center of mass. Galaxies contain varying amounts of star systems, star clusters and types of interstellar clouds. In between these objects is a sparse interstellar medium of gas, dust, and cosmic rays. Dark matter appears to account for around 90% of the mass of most galaxies. Observational data suggests that supermassive black holes may exist at the center of many, if not all, galaxies.

They are thought to be the primary driver of active galactic nuclei found at the core of some galaxies. The Milky Way galaxy appears to harbor at least one such object. Galaxies have been historically categorized according to their apparent shape; usually referred to as their visual morphology. A common form is the elliptical galaxy, which has an ellipse-shaped light profile. Spiral galaxies are disk-shaped with dusty, curving arms. Those with irregular or unusual shapes are known as irregular galaxies and typically originate from disruption by the gravitational pull of neighboring galaxies. Such interactions between nearby galaxies, which may ultimately result in a merging, sometimes induce significantly increased incidents of star formation leading starburst galaxys. Smaller galaxies lacking a coherent structure are referred to as irregular galaxies. There are probably more than 170 billion (1.7 × 1011) galaxies in the observable universe. Most are 1,000 to 100,000 parsecs in diameter and usually separated by distances on the order of millions of parsecs (or megaparsecs). Intergalactic space (the space between galaxies) is filled with a tenuous gas of an average density less than one atom per cubic meter.

The majority of galaxies are organized into a hierarchy of associations known as groups and clusters, which, in turn usually form larger superclusters. At the largest scale, these associations are generally arranged into sheets and filaments, which are surrounded by immense voids. Observation history The realization that we live in a galaxy, and that there were, in fact, many other galaxies, parallels discoveries that were made about the Milky Way and other nebulae in the night sky. The Milky Way The Greek philosopher Democritus (450–370 BC) proposed that the bright band on the night sky known as the Milky Way might consist of distant stars. Aristotle (384–322 BC), however, believed the Milky Way to be caused by "the ignition of the fiery exhalation of some stars which were large, numerous and close together" and that the "ignition takes place in the upper part of the atmosphere, in the region of the world which is continuous with the heavenly motions." The Neoplatonist philosopher Olympiodorus the Younger (c.

495–570 AD) criticized this view, arguing that if the Milky Way were sublunary it should appear different at different times and places on the Earth, and that it should have parallax, which it does not. In his view, the Milky Way was celestial. This idea would be influential later in the Islamic world. The Arabian astronomer, Alhazen (965–1037), made the first attempt at observing and measuring the Milky Way's parallax,and he thus "determined that because the Milky Way had no parallax, it was very remote from the Earth and did not belong to the atmosphere." The Persian astronomer Abū Rayhān al-Bīrūnī (973–1048) proposed the Milky Way galaxy to be "a collection of countless fragments of the nature of nebulous stars." The Andalusian astronomer Ibn Bajjah ("Avempace", d.

1138) proposed that the Milky Way was made up of many stars that almost touch one another and appear to be a continuous image due to the effect of refraction from sublunary material, citing his observation of the conjunction of Jupiter and Mars as evidence of this occurring when two objects are near. The Syrian-born Ibn Qayyim Al-Jawziyya (1292–1350) proposed the Milky Way galaxy to be "a myriad of tiny stars packed together in the sphere of the fixed stars". Actual proof of the Milky Way consisting of many stars came in 1610 when Galileo Galilei used a telescope to study the Milky Way and discovered that it is composed of a huge number of faint stars. In 1750 Thomas Wright, in his An original theory or new hypothesis of the Universe, speculated (correctly) that the galaxy might be a rotating body of a huge number of stars held together by gravitational forces, akin to the solar system but on a much larger scale. The resulting disk of stars can be seen as a band on the sky from our perspective inside the disk.

In a treatise in 1755, Immanuel Kant elaborated on Wright's idea about the structure of the Milky Way. The first attempt to describe the shape of the Milky Way and the position of the Sun in it was carried out by William Herschel in 1785 by carefully counting the number of stars in different regions of the sky. He produced a diagram of the shape of the galaxy with the solar system close to the center. Using a refined approach, Kapteyn in 1920 arrived at the picture of a small (diameter about 15 kiloparsecs) ellipsoid galaxy with the Sun close to the center. A different method by Harlow Shapley based on the cataloguing of globular clusters led to a radically different picture: a flat disk with diameter approximately 70 kiloparsecs and the Sun far from the center. Both analyses failed to take into account the absorption of light by interstellar dust present in the galactic plane, but after Robert Julius Trumpler quantified this effect in 1930 by studying open clusters, the present picture of our galaxy, the Milky Way, emerged.

Modern research In 1944, Hendrik van de Hulst predicted microwave radiation at a wavelength of 21 cm resulting from interstellar atomic hydrogen gas; this radiation was observed in 1951. The radiation allowed for much improved study of the Milky Way Galaxy, since it is not affected by dust absorption and its Doppler shift can be used to map the motion of the gas in the Galaxy. These observations led to the postulation of a rotating bar structure in the center of the Galaxy. With improved radio telescopes, hydrogen gas could also be traced in other galaxies. In the 1970s it was discovered in Vera Rubin's study of the rotation speed of gas in galaxies that the total visible mass (from the stars and gas) does not properly account for the speed of the rotating gas. This galaxy rotation problem is thought to be explained by the presence of large quantities of unseen dark matter. Beginning in the 1990s, the Hubble Space Telescope yielded improved observations. Among other things, it established that the missing dark matter in our galaxy cannot solely consist of inherently faint and small stars.

The Hubble Deep Field, an extremely long exposure of a relatively empty part of the sky, provided evidence that there are about 125 billion (1.25×1011) galaxies in the universe. Improved technology in detecting the spectra invisible to humans (radio telescopes, infrared cameras, and x-ray telescopes) allow detection of other galaxies that are not detected by Hubble. Particularly, galaxy surveys in the Zone of Avoidance have revealed a number of new galaxies. Dwarfs Galaxy Despite the prominence of large elliptical and spiral galaxies, most galaxies in the universe appear to be dwarf galaxies. These galaxies are relatively small when compared with other galactic formations, being about one hundredth the size of the Milky Way, containing only a few billion stars. Ultra-compact dwarf galaxies have recently been discovered that are only 100 parsecs across. Many dwarf galaxies may orbit a single larger galaxy; the Milky Way has at least a dozen such satellites, with an estimated 300–500 yet to be discovered. Dwarf galaxies may also be classified as elliptical, spiral, or irregular. Since small dwarf ellipticals bear little resemblance to large ellipticals, they are often called dwarf spheroidal galaxies instead.

A study of 27 Milky Way neighbors found that in all dwarf galaxies, the central mass is approximately 10 million solar masses, regardless of whether the galaxy has thousands or millions of stars. This has led to the suggestion that galaxies are largely formed by dark matter, and that the minimum size may indicate a form of warm dark matter incapable of gravitational coalescence on a smaller scale. Universe, Galaxies And Stars - Astronomy And Space News. Universe Galaxies and Stars Exploring The Universe, Science and Astronomy. Welcome to universe, galaxies and stars. The universe is commonly defined as the totality of everything that exists - including all physical space, time , matter and energy , the planets , stars , galaxies , and the contents of intergalactic space, although this usage may differ with the context. The term universe may be used in slightly different contextual senses, denoting such concepts as the cosmos , the world, or nature . Observations of earlier stages in the development of the universe, which can be seen at great distances, suggest that the universe has been governed by the same physical laws and constants throughout most of its extent and history. Some physicists have speculated that the universe is one among a numerous number of universes in the multiverse theory.

Galaxies are massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas dust, and an important but poorly understood component tentatively dubbed dark matter. The name is from the Greek word galaxias, literally meaning "milky", a reference to the Milky Way galaxy. Typical galaxies range from dwarfs with as few as ten million (107) stars, up to giants with a hundred trillion (1014) stars - all orbiting the galaxy's center of mass. Galaxies may contain many star systems, star clusters, and various interstellar clouds. The Sun is one of the stars in the Milky Way galaxy ; the Solar System includes the Earth and all the other objects that orbit the Sun . Historically, galaxies have been categorized according to their apparent shape (usually referred to as their visual morphology). A common form is the elliptical galaxy, which has an ellipse-shaped light profile. Spiral galaxies are disk-shaped assemblages with dusty, curving arms. Galaxies with irregular or unusual shapes are known as irregular galaxies, and typically result from disruption by the gravitational pull of neighboring galaxies.

Such interactions between nearby galaxies, which may ultimately result in galaxies merging, may induce episodes of significantly increased star formation, producing what is called a starburst galaxy. Small galaxies that lack a coherent structure could also be referred to as irregular galaxies . Stars are massive, luminous balls of plasma held together by gravity . At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth. Other stars are visible from Earth during the night when they are not outshone by the Sun or blocked by atmospheric phenomena. Historically, the most prominent stars on the celestial sphere were grouped together into constellations and asterisms, and the brightest stars gained proper names. Extensive catalogues of stars have been assembled by astronomers, which provide standardized star designations. For at least a portion of its life, a star shines due to thermonuclear fusion of hydrogen in its core releasing energy that traverses the star's interior and then radiates into outer space. Almost all naturally occurring elements heavier than helium were created by stars, either via stellar nucleosynthesis during their lifetimes or by supernova nucleosynthesis when stars explode.

Astronomers can determine the mass , age, chemical composition and many other properties of a star by observing its spectrum, luminosity and motion through space . The total mass of a star is the principal determinant in its evolution and eventual fate. Other characteristics of a star are determined by its evolutionary history, including diameter, rotation, movement and temperature. A plot of the temperature of many stars against their luminosities, known as a Hertzsprung-Russell diagram (H?R diagram), allows the age and evolutionary state of a star to be determined. A star begins as a collapsing cloud of material composed primarily of hydrogen, along with helium and trace amounts of heavier elements. Once the stellar core is sufficiently dense, some of the hydrogen is steadily converted into helium through the process of nuclear fusion. The remainder of the star's interior carries energy away from the core through a combination of radiative and convective processes. The star's internal pressure prevents it from collapsing further under its own gravity. Once the hydrogen fuel at the core is exhausted, those stars having at least 0.4 times the mass of the Sun expand to become a red giant, in some cases fusing heavier elements at the core or in shells around the core.

The star then evolves into a degenerate form, recycling a portion of the matter into the interstellar environment, where it will form a new generation of stars with a higher proportion of heavy elements. Latest Addition To Universe Galaxies And Stars: Star Formation In The Universe About universe, galaxies and stars. Universe galaxies and stars is primarily at website about the universe. However, as so many of our surfers have asked for other subjects, universe, galaxies and stars has decided to expand our content. We hope, at universe, galaxies and stars to create a website packed with interesting information. To reflect this, universe, galaxies and stars might under go a name change soon. We hope to bring all of you, a comprehensive website packed with feature rich knowledge about a wide and varied range of topics. However, our commitment to universe subjects will not suffer as a result. The universe, galaxies and stars will still head our program of dedicated information. But, as we are sure you are aware, just concentrating on the one subject can get a little boring. As the philosopher once said, variety is the spice of life! With this in mind, we hope to chose content that expands the imagination.

We want to make our surfers think, to question and understand the extent of knowledge out there. If there is a topic you particularly like, why not drop us a line, and we'll see if we can't include it at a later date. But, in the mean time, why not have a look in the feature-paced pages of our website and include a link so others can experience the great content available. Galaxy – 月與魚的對話 瀲灩中的相得忘形 Galaxy A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter.[1][2] The name is from the Greek root galaxias [γαλαξίας], meaning “milky,” a reference to the Milky Way galaxy. Typical galaxies range from dwarfs with as few as ten million[3] (107) stars up to giants with a hundred trillion[4] (1014) stars, all orbiting the galaxy’s center of mass. Galaxies may contain many multiple star systems, star clusters, and various interstellar clouds.

The Sun is one of the stars in the Milky Way galaxy; the Solar System includes the Earth and all the other objects that orbit the Sun. Historically, galaxies have been categorized according to their apparent shape (usually referred to as their visual morphology). A common form is the elliptical galaxy,[5] which has an ellipse-shaped light profile. Spiral galaxies are disk-shaped assemblages with dusty, curving arms. Galaxies with irregular or unusual shapes are known as irregular galaxies, and typically result from disruption by the gravitational pull of neighboring galaxies. Such interactions between nearby galaxies, which may ultimately result in galaxies merging, may induce episodes of significantly increased star formation, producing what is called a starburst galaxy.

Small galaxies that lack a coherent structure could also be referred to as irregular galaxies.[6] There are probably more than 170 billion (1.7 × 1011) galaxies in the observable universe.[7][8] Most galaxies are 1,000 to 100,000[9] parsecs in diameter and are usually separated by distances on the order of millions of parsecs (or megaparsecs).[10] Intergalactic space (the space between galaxies) is filled with a tenuous gas of an average density less than one atom per cubic meter. The majority of galaxies are organized into a hierarchy of associations called clusters, which, in turn, can form larger groups called superclusters. These larger structures are generally arranged into sheets and filaments, which surround immense voids in the universe.[11] Although it is not yet well understood, dark matter appears to account for around 90% of the mass of most galaxies. Observational data suggests that supermassive black holes may exist at the center of many, if not all, galaxies. They are proposed to be the primary cause of active galactic nuclei found at the core of some galaxies.

The Milky Way galaxy appears to harbor at least one such object within its nucleus.[12] 重力相繫(gravitationally bound) Galaxy - YouTube Galaxy Want to watch this again later? Sign in to add this video to a playlist. Need to report the video? Sign in to report inappropriate content. The interactive transcript could not be loaded. Loading... Rating is available when the video has been rented. This feature is not available right now. Please try again later. Published on Mar 9, 2014 A galaxy is a massive, gravitationally bound system consisting of stars, stellar remnants, an interstellar medium of gas and dust, and dark matter, an important but poorly understood component. The word galaxy is derived from the Greek galaxias , literally "milky", a reference to the Milky Way. Examples of galaxies range from dwarfs with as few as ten million stars to giants with one hundred trillion stars, each orbiting their galaxy's own center of mass. Galaxies contain varying numbers of planets, star systems, star clusters and types of interstellar clouds. In between these objects is a sparse interstellar medium of gas, dust, and cosmic rays. Supermassive black holes reside at the center of most galaxies.

They are thought to be the primary driver of active galactic nuclei found at the core of some galaxies. The Milky Way galaxy is known to harbor at least one such object. Galaxies have been historically categorized according to their apparent shape, usually referred to as their visual morphology. A common form is the elliptical galaxy, which has an ellipse-shaped light profile. Spiral galaxies are disk-shaped with dusty, curving arms. Those with irregular or unusual shapes are known as irregular galaxies and typically originate from disruption by the gravitational pull of neighboring galaxies. Such interactions between nearby galaxies, which may ultimately result in a merger, sometimes induce significantly increased incidents of star formation leading to starburst galaxies. Smaller galaxies lacking a coherent structure are referred to as irregular galaxies. There are probably more than 170 billion galaxies in the observable universe. Most are 1,000 to 100,000 parsecs in diameter and usually separated by distances on the order of millions of parsecs (or megaparsecs). Intergalactic space (the space between galaxies) is filled with a tenuous gas of an average density less than one atom per cubic meter.

The majority of galaxies are organized into a hierarchy of associations known as galaxy groups and clusters, which, in turn usually form larger superclusters. At the largest scale, these associations are generally arranged into sheets and filaments, which are surrounded by immense voids. In October 2013, z8 GND 5296 was confirmed to be the most distant galaxy yet discovered whose redshift was measured through the Lyman-alpha emission line of hydrogen, at a distance of approximately 13.1 billion light-years from Earth. The galaxy appears to astronomers as it was "just 700 million years after the Big Bang, when the universe was only about 5 percent of its current age of 13.8 billion years." It produces stars at a phenomenal rate of about 300 suns per year in mass and has a redshift of 7.51. Etymology This video targeted to blind users. Attribution: Article text available under CC-BY-SA Public domain image source in video Category Phys.org - galaxies galaxies You know how long it takes to pack the car to go on holidays.

But there's a moment when you're all in, everyone has their seatbelt on, you pull out of the drive and you're off. 23 hours ago in Astronomy 8 23 hours ago in Astronomy report 448 An international team of astronomers, led by Christopher Conselice, Professor of Astrophysics at the University of Nottingham, have found that the universe contains at least 2 trillion galaxies, ten times more than previously ... Jan 16, 2017 in Astronomy 5764 The beautiful spiral galaxy visible in the center of the image is known as RX J1140.1+0307, a galaxy in the Virgo constellation imaged by the NASA/ESA Hubble Space Telescope, and it presents an interesting puzzle. At first ... Jan 13, 2017 in Astronomy 243 An instrument designed to image the vast web of gas that connects galaxies in the universe has been shipped from Los Angeles to Hawaii, where it will be integrated into the W. M. Keck Observatory. Jan 12, 2017 in Astronomy 23 In roughly four billion years, the Milky Way will be no more.

Jan 12, 2017 in Astronomy 216 The 11 farthest known stars in our galaxy are located about 300,000 light-years from Earth, well outside the Milky Way's spiral disk. New research by Harvard astronomers shows that half of those stars might have been ripped ... Jan 11, 2017 in Astronomy 372 Astronomers led by David Sobral and Jorryt Matthee, of the Universities of Lancaster in the UK and Leiden in the Netherlands have discovered giant halos around early Milky Way type galaxies, made of photons (elementary particles ... Jan 11, 2017 in Astronomy 457 The American Institute of Physics (AIP) and the American Astronomical Society (AAS) announced today, on behalf of the Heineman Foundation for Research, Educational, Charitable, and Scientific Purposes, that California astrophysicist ... Jan 09, 2017 in Astronomy 14 Galaxies evolve over billions of years in part through the activity of star formation and their supermassive nuclear black holes, and also by mergers with other galaxies.

Some features of galaxies, in particular the strong ... Jan 09, 2017 in Astronomy 26 Next » Galaxy A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The name is from the Greek root galaxias [γαλαξίας], meaning "milky," a reference to the Milky Way galaxy. Typical galaxies range from dwarfs with as few as ten million (107) stars up to giants with one trillion (1012) stars, all orbiting the galaxy's center of mass. Galaxies can also contain many multiple star systems, star clusters, and various interstellar clouds. The Sun is one of the stars in the Milky Way galaxy; the Solar System includes the Earth and all the other objects that orbit the Sun. Historically, galaxies have been categorized according to their apparent shape (usually referred to as their visual morphology). A common form is the elliptical galaxy, which has an ellipse-shaped light profile. Spiral galaxies are disk-shaped assemblages with curving, dusty arms.

Galaxies with irregular or unusual shapes are known as peculiar galaxies, and typically result from disruption by the gravitational pull of neighboring galaxies. Such interactions between nearby galaxies, which may ultimately result in galaxies merging, may induce episodes of significantly increased star formation, producing what is called a starburst galaxy. Small galaxies that lack a coherent structure could also be referred to as irregular galaxies. There are probably more than 100 billion (1011) galaxies in the observable universe. Most galaxies are 1,000 to 100,000 parsecs in diameter and are usually separated by distances on the order of millions of parsecs (or megaparsecs). Intergalactic space (the space between galaxies) is filled with a tenuous gas of an average density less than one atom per cubic meter. The majority of galaxies are organized into a hierarchy of associations called clusters, which, in turn, can form larger groups called superclusters. These larger structures are generally arranged into sheets and filaments, which surround immense voids in the universe. Although it is not yet well understood, dark matter appears to account for around 90% of the mass of most galaxies.

Observational data suggests that supermassive black holes may exist at the center of many, if not all, galaxies. They are proposed to be the primary cause of active galactic nuclei found at the core of some galaxies. The Milky Way galaxy appears to harbor at least one such object within its nucleus. This text uses material from Wikipedia , licensed under CC BY-SA Galaxies - Galactic Center Galaxies A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter literally meaning "milky", a reference to the Milky Way. Galaxies range in size from dwarfs with just a few billion stars to giants with one hundred trillion stars each orbiting its galaxy's center of mass. Galaxies are categorized according to their visual morphology as elliptical, spiral and irregular. Many galaxies are thought to have black holes at their active centers. The Milky Way's central black hole, known as Sagittarius A*, has a mass four million times greater than the Sun.

As of March 2016, GN-z11 is the oldest and most distant observed galaxy with a co-moving distance of 32 billion light-years from Earth, and observed as it existed just 400 million years after the Big Bang. Previously, as of July 2015, EGSY8p7 was the most distant known galaxy, estimated to have a light travel distance of 13.2 billion light-years away. Approximately 200 billion or, more recently, at least 2 trillion galaxies exist in the observable universe. Most of the galaxies are 1,000 to 100,000 parsecs in diameter and usually separated by distances on the order of millions of parsecs (or megaparsecs). The space between galaxies is filled with a tenuous gas having an average density of less than one atom per cubic meter. The majority of galaxies are gravitationally organized into associations known as galaxy groups, clusters, and superclusters. At the largest scale, these associations are generally arranged into sheets and filaments surrounded by immense voids. The largest structure of galaxies yet recognised is a cluster of superclusters, that has been named Laniakea.

Read more Antennae Galaxies are a pair of interacting galaxies in the constellation Corvus. Dark Galaxies contain very few, or no stars. Held together by dark matter, they may also contain gas and dust. No dark galaxy with a black hole as a center has yet been discovered. Dwarf Galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Way's 200-400 billion stars. Elliptical Galaxies have an ellipse-shaped light profile. Interacting Galaxy or Colliding Galaxies are the result of one galaxy's gravity disturbing another galaxy. Irregular Galaxies do not have a regular shape. Lenticular Galaxies are intermediate between an elliptical galaxy and a spiral galaxy in galaxy morphological classification schemes. Luminous Infrared Galaxies (LIRG) emit more than 1011 solar luminosities in the far-infrared part of the electromagnetic spectrum. Peculiar Galaxies have irregular or unusual shapes typically resulting from disruption by the gravitational pull of neighboring galaxies. Ring Galaxies have a ring-like appearance. The ring consists of massive, relatively young blue stars, which are extremely bright.

Spiral Galaxies are disk-shaped assemblages with dusty, curving arms. The Whirlpool Galaxy is an interacting grand-designspiral galaxy located at a distance of approximately 23 million light-years in the constellation Canes Venatici. Dark Matter appears to account for about 90% of the mass of most galaxies. Observational data suggests that supermassive black holes may exist at the center of many, if not all, galaxies. They are proposed to be the primary cause of active galactic nuclei found at the core of some galaxies. The Milky Way Galaxy appears to harbor at least one such object within its nucleus. Galactic Center White Dwarfs in Milky Way's Central Hub. A view of the night sky near Sagittarius, enhanced to show better contrast and detail in the dust lanes. The principal stars in Sagittarius are indicated in red. Spiraling arm The Galactic Center is the rotational center of the Milky Way.

The estimates for its location range from 7.6 to 8.7 kiloparsecs (about 25,000 to 28,000 lightyears) from Earth in the direction of the constellations Sagittarius, Ophiuchus, and Scorpius where the Milky Way appears brightest. There is strong evidence consistent with the existence of a supermassive black hole at the Galactic Center of the Milky Way. Scientists at the Max Planck Institute for Extraterrestrial Physics in Germany using Chilean telescopes have confirmed the existence of a supermassive black hole at the Galactic Center, on the order of 4.3 million solar masses. A complex astronomical radio source Sagittarius A appears to be located almost exactly at the Galactic Center (approx. 18 hrs, -29 deg), and contains an intense compact radio source, Sagittarius A*, which coincides with a supermassive black hole at the center of the Milky Way. Accretion of gas onto the black hole, probably involving a disk around it, would release energy to power the radio source, itself much larger than the black hole. The latter is too small to see with present instruments.

Read more Black Hole at the galactic center Astronomers found the first real evidence for a supermassive black hole in our Galaxy in 1974 when they detected strong radio emissions coming from a spot they called Sagittarius A*. These radio waves are a kind of �smoking gun,� hinting there is a disk of material orbiting around a massive, unseen object. The black hole at Sagittarius A* seems to have a mass of around 4 million times that of the Sun. But black holes are so dense that the size of the corresponding black hole would only be about about 20 times the size of the Sun. That is far too small for us to see from Earth, even with our most powerful telescopes. Since 1995, astronomers have been able to use infrared telescopes to observe individual stars in the Galactic Center right in the Sagittarius A* region. By repeating the observations year after year, the motions of these stars can be mapped out. Normally stars move very slowly over time, but these stars are whipping around at such astonishing speeds we can see their positions shift year by year.

They trace out the elliptical orbits we would expect to see if they were orbiting a massive, unseen object. One of the stars, known as S0-102, completed a full 409 billion-mile orbit in a mere 11.5 years, traveling at over 3000 miles per second. The shapes of the orbits of these stars confirms they are all orbiting a single small object, and the timing of the orbits allows astronomers to calculate that the object's mass is 4 million times greater than that of our Sun. To date, a black hole is the only theory of physics that can explain that observation. It almost sounds like astronomers have done the impossible. Using infrared light, they have measured the mass of a black hole that, by definition, cannot be seen at any wavelength of light at all.

UNITS 5-8 at Northville High School - StudyBlue 1) the inner core (mostly solid iron) 2) the outer core (mostly liquid iron) 3) the Mantle (solid Fe/Mg silicates) 4) the Crust (solid K/Na silicates) 5) an outer film of water and gases (hydrosphere & atmosphere) Earth´s Layers The Earth is separated into layers based on mechanical properties in addition to composition. The topmost layer is the lithosphere (crust and solid portion of the upper mantle). The lithosphere essentially floats atop a semi-liquid layer known as the asthenosphere. This layer allows the solid lithosphere to move around since the asthenosphere is much weaker than the lithosphere. Core The last layer is the core, which is separated into the liquid outer core and the solid inner core. The outer core is 2300 km thick and the inner core is 1200 km thick. The outer core is composed mainly of a nickel-iron alloy, while the inner core is almost entirely composed of iron. Earth's magnetic field is believed to be controlled by the liquid outer core.

Mantle 1 The mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density. The interior of the Earth is chemically divided into layers. Earth's mantle is a rocky shell about 2,890 km (1,800 mi) thick that constitutes about 84% of Earth's volume. It is predominantly solid and encloses the iron-rich hot core, which occupies about 15% of Earth's volume. Crust The outermost layer of the Earth is the crust. This comprises the continents and ocean basins. The crust has a variable thickness, being 35-70 km thick in the continents and 5-10 km thick in the ocean basins. The crust is composed mainly of alumino-silicates. Plate Tectonics Plate tectonics (from the Late Latin tectonicus, from the Greek: τεκτονικός "pertaining to building") is a scientific theory that describes the large scale motions of Earth's lithosphere.

The theory builds on the concepts of continental drift, developed during the first decades of the 20th century, and accepted by the majority of the geoscientific community when the concepts of seafloor spreading were developed in the late 1950s and early 1960s. Continental Drift Continental drift is the movement of the Earth's continents relative to each other. The hypothesis that continents 'drift' was first put forward by Abraham Ortelius in 1596 and was fully developed by Alfred Wegener in 1912. However, it was not until the development of the theory of plate tectonics in the 1960s, that a sufficient geological explanation of that movement was found. Radiometric Dating Radiometric dating is a technique used to date materials such as rocks, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates. It is the principal source of information about the absolute age of rocks and other geological features, including the age of the Earth itself.

Carbon 14 Carbon-14, 14C, or radiocarbon, is a radioactive isotope of carbon with a nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues (1949), to date archaeological, geological, and hydrogeological samples. Absolute Dating Absolute dating is the process of determining an approximate computed age in archaeology and geology. Some scientists prefer the terms chronometric or calendar dating, as use of the word "absolute" implies an unwarranted certainty and precision. Absolute dating provides a computed numerical age in contrast with relative dating which provides only an order of events. Relative Dating Relative dating is the science determining the relative order of past events, without necessarily determining their absolute age. In geology rock or superficial deposits, fossils and lithologies can be used to correlate one stratigraphic column with another. Threshold 2 Before stars formed, the Universe was relatively cool and uniform. Stars were an important new form of complexity because they introduced long-lasting hot sports where even more complex things could form. Stars also gave the Universe more structure by gathering together to form galaxies, clusters and super-clusters.

Threshold 3 The Universe was a relatively simple place until the first stars died. You couldn´t make much with just Hydrogen and Helium. Dying stars were another story. They created the extremely high temperatures necessary to fuse nuclei and create new chemical elements. These all had distinct properties and provided the raw material for a nearly infinite number of new possibilities. Threshold 4 Even after millions of supernovae exploded to create new elements, most of the universe still consisted of Hydrogen, Helium & empty space. Planets, which formed from leftover debris around newborn stars, contained much greater chemical complexity than anything else in the universe. On rocky planets like our earth, even more remarkable things could happen. Stars 2 A star shines due to thermonuclear fusion of hydrogen in its core releasing energy that traverses the star's interior and then radiates into outer space. Almost all naturally occurring elements heavier than helium were created by stars, either via stellar nucleosynthesis during their lifetimes or by supernova nucleosynthesis when stars explode. Alfred Wegener (1880-1930) Alfred Lothar Wegener was a German scientist, geophysicist and meteorologist.

He is most notable for his theory of continental drift (Kontinentalverschiebung), proposed in 1912, which hypothesized that the continents were slowly drifting around the Earth. However, his hypothesis was not widely accepted until the 1950s, when numerous discoveries such as palaeomagnetism provided strong support for his hypothesis of continental drift. Mantle 2 The next layer is the mantle, which is composed mainly of ferro-magnesium silicates. It is about 2900 km thick, and is separated into the upper and lower mantle. This is where most of the internal heat of the Earth is located. Large convective cells in the mantle circulate heat and may drive plate tectonic processes. Asteroid Asteroids (from Greek ἀστήρ 'star' and εἶδος 'like, in form') are a class of small Solar System bodies in orbit around the Sun. This term has historically been applied to any astronomical object orbiting the Sun that did not show the disk of a planet.

Accretion -- Nebular Theory In the nebular theory, accretion refers to the collision and sticking of cooled microscopic dust and ice particles electrostatically, in protoplanetary discs and Gas giant protoplanet systems, eventually leading to planetesimals which gravitationally accrete more small particles and other planetesimals. Sun -- Chemical Composition Chemically, about three quarters of the Sun's mass consists of hydrogen, while the rest is mostly helium. The rest of it (1.69%, 5,628 times the mass of Earth) consists of heavier elements, including oxygen, carbon, neon, iron, and others. Solar System -- Inner Planets Of the many objects that orbit the Sun, most of the mass is contained within eight relatively solitary planets[e] whose orbits are almost circular and lie within a nearly flat disc called the ecliptic plane. The four smaller inner planets, Mercury, Venus, Earth and Mars, also called the terrestrial planets, are primarily composed of rock and metal. Solar System -- Outer Planets The four outer planets, the gas giants, are substantially more massive than the terrestrials.

The two largest, Jupiter and Saturn, are composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are composed largely of ices, such as water, ammonia and methane, and are often referred to separately as "ice giants". Asteroid Belt Asteroids are mostly small Solar System bodies composed mainly of refractory rocky and metallic minerals, with some ice. The asteroid belt occupies the orbit between Mars and Jupiter, between 2.3 and 3.3 AU from the Sun. It is thought to be remnants from the Solar System's formation that failed to coalesce because of the gravitational interference of Jupiter. Mercury Mercury (0.4 AU from the Sun) is the closest planet to the Sun and the smallest planet in the Solar System (0.055 Earth masses). Mercury has no natural satellites, and its only known geological features besides impact craters are lobed ridges or rupes, probably produced by a period of contraction early in its history. Mercury's almost negligible atmosphere consists of atoms blasted off its surface by the solar wind.

Venus Venus (0.7 AU from the Sun) is close in size to Earth (0.815 Earth masses), and, like Earth, has a thick silicate mantle around an iron core, a substantial atmosphere and evidence of internal geological activity. However, it is much drier than Earth and its atmosphere is ninety times as dense. Venus has no natural satellites. It is the hottest planet, with surface temperatures over 400 °C. Mars Mars (1.5 AU from the Sun) is smaller than Earth and Venus (0.107 Earth masses). It possesses an atmosphere of mostly carbon dioxide with a surface pressure of 6.1 millibars (roughly 0.6 percent that of the Earth's). Its surface, peppered with vast volcanoes such as Olympus Mons and rift valleys such as Valles Marineris, shows geological activity that may have persisted until as recently as 2 million years ago. Its red colour comes from iron oxide (rust) in its soil. Jupiter Jupiter (5.2 AU), at 318 Earth masses, is 2.5 times the mass of all the other planets put together. It is composed largely of hydrogen and helium.

Jupiter's strong internal heat creates a number of semi-permanent features in its atmosphere, such as cloud bands and the Great Red Spot.Jupiter has 64 known satellites. The four largest, Ganymede, Callisto, Io, and Europa. Saturn Saturn (9.5 AU), distinguished by its extensive ring system, has several similarities to Jupiter, such as its atmospheric composition and magnetosphere. Although Saturn has 60% of Jupiter's volume, it is less than a third as massive, at 95 Earth masses, making it the least dense planet in the Solar System. The rings of Saturn are made up of small ice and rock particles. Uranus Uranus (19.6 AU), at 14 Earth masses, is the lightest of the outer planets. Uniquely among the planets, it orbits the Sun on its side; its axial tilt is over ninety degrees to the ecliptic. It has a much colder core than the other gas giants, and radiates very little heat into space. Uranus has 27 known satellites, the largest ones being Titania, Oberon, Umbriel, Ariel and Miranda.

Neptune Neptune (30 AU), though slightly smaller than Uranus, is more massive (equivalent to 17 Earths) and therefore more dense. It radiates more internal heat, but not as much as Jupiter or Saturn. Neptune has 13 known satellites. The largest, Triton, is geologically active, with geysers of liquid nitrogen. Triton is the only large satellite with a retrograde orbit. Neptune is accompanied in its orbit by a number of minor planets, termed Neptune Trojans, that are in 1:1 resonance with it. Centaurs The centaurs are icy comet-like bodies with a semi-major axis greater than Jupiter's (5.5 AU) and less than Neptune's (30 AU). The largest known centaur, 10199 Chariklo, has a diameter of about 250 km. The first centaur discovered, 2060 Chiron, has also been classified as comet (95P) since it develops a coma just as comets do when they approach the Sun. Protons The proton is a subatomic particle with the symbol p or p+ and a positive electric charge of 1 elementary charge.

One or more protons are present in thenucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number. In the standard model of particle physics, the proton is a hadron, composed of quarks. Geologic Time The largest defined unit of time is the supereon, composed of eons. Eons are divided into eras, which are in turn divided intoperiods, epochs and ages. The terms eonothem, erathem, system, series, and stage are used to refer to the layers of rock that correspond to these periods of geologic time. * The material on this site is created by StudyBlue users. StudyBlue is not affiliated with, sponsored by or endorsed by the academic institution or instructor. Words From Our Students "StudyBlue is great for studying. I love the study guides, flashcards and quizzes. So extremely helpful for all of my classes!" Alice , Arizona State University "I'm a student using StudyBlue, and I can 100% say that it helps me so much. Study materials for almost every subject in school are available in StudyBlue.

It is so helpful for my education!" Tim , University of Florida "StudyBlue provides way more features than other studying apps, and thus allows me to learn very quickly!??I actually feel much more comfortable taking my exams after I study with this app. It's amazing!" Jennifer , Rutgers University "I love flashcards but carrying around physical flashcards is cumbersome and simply outdated. StudyBlue is exactly what I was looking for!" Justin , LSU Design elements - Galaxies | Education | Aerospace - Design Elements | Galaxies Design elements - Galaxies Design elements - Galaxies The vector stencils library "Galaxies" contains 15 galaxy symbols for drawing astronomical diagrams. "A galaxy is a massive, gravitationally bound system consisting of stars, stellar remnants, an interstellar medium of gas and dust, and dark matter, an important but poorly understood component. The word galaxy is derived from the Greek galaxias ..., literally "milky", a reference to the Milky Way. Examples of galaxies range from dwarfs with as few as ten million (10^7) stars to giants with one hundred trillion (10^14) stars, each orbiting their galaxy's own center of mass.

Galaxies contain varying numbers of planets, star systems, star clusters and types of interstellar clouds. In between these objects is a sparse interstellar medium of gas, dust, and cosmic rays. Supermassive black holes reside at the center of most galaxies. They are thought to be the primary driver of active galactic nuclei found at the core of some galaxies. The Milky Way galaxy is known to harbor at least one such object. Galaxies have been historically categorized according to their apparent shape, usually referred to as their visual morphology. A common form is the elliptical galaxy, which has an ellipse-shaped light profile. Spiral galaxies are disk-shaped with dusty, curving arms. Those with irregular or unusual shapes are known as irregular galaxies and typically originate from disruption by the gravitational pull of neighboring galaxies. Such interactions between nearby galaxies, which may ultimately result in a merger, sometimes induce significantly increased incidents of star formation leading to starburst galaxies. Smaller galaxies lacking a coherent structure are referred to as irregular galaxies." [Galaxy. Wikipedia] The example "Design elements - Galaxies" was created using the ConceptDraw PRO diagramming and vector drawing software extended with the Astronomy solution from the Science and Education area of ConceptDraw Solution Park.

Galaxy symbols Aerospace illustration template contains vector clipart of space objects: planets and galaxies, satellites and space stations, rockets and shuttles, planet rovers and radio telescopes, etc. Use it to draw spacecraft illustrations. "A spacecraft (or spaceship) is a vehicle, vessel or machine designed to fly in outer space. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo. On a sub-orbital spaceflight, a spacecraft enters space and then returns to the surface, without having gone into an orbit. For orbital spaceflights, spacecraft enter closed orbits around the Earth or around other celestial bodies. Spacecraft used for human spaceflight carry people on board as crew or passengers from start or on orbit (space stations) only, while those used for robotic space missions operate either autonomously or telerobotically. Robotic spacecraft used to support scientific research are space probes. Robotic spacecraft that remain in orbit around a planetary body are artificial satellites. Orbital spacecraft may be recoverable or not. By method of reentry to Earth they may be divided in non-winged space capsules and winged spaceplanes." [Spacecraft.

Wikipedia] The Aerospace illustration template is included in the Aerospace and Transport solution from Illustration area of ConceptDraw Solution Park. Design elements - Constellations except Zodiac, Northern and Southern The vector stencils library "Constellations except Zodiac, Northern and Southern" contains 47 star constellation maps. "A star chart or star map is a map of the night sky. Astronomers divide these into grids to use them more easily. They are used to identify and locate astronomical objects such as stars, constellations and galaxies. They have been used for human navigation since time immemorial. Note that a star chart differs from an astronomical catalog, which is a listing or tabulation of astronomical objects for a particular purpose. A planisphere is a type of star chart." [Star chart. Wikipedia] The star charts example "Design elements - Constellations except Zodiac, Northern and Southern" was created using the ConceptDraw PRO diagramming and vector drawing software extended with the Astronomy solution from the Science and Education area of ConceptDraw Solution Park. Design elements - Galaxies Design elements - Galaxies The vector stencils library "Galaxies" contains 15 galaxy symbols for drawing astronomical diagrams.

"A galaxy is a massive, gravitationally bound system consisting of stars, stellar remnants, an interstellar medium of gas and dust, and dark matter, an important but poorly understood component. The word galaxy is derived from the Greek galaxias ..., literally "milky", a reference to the Milky Way. Examples of galaxies range from dwarfs with as few as ten million (10^7) stars to giants with one hundred trillion (10^14) stars, each orbiting their galaxy's own center of mass. Galaxies contain varying numbers of planets, star systems, star clusters and types of interstellar clouds. In between these objects is a sparse interstellar medium of gas, dust, and cosmic rays. Supermassive black holes reside at the center of most galaxies. They are thought to be the primary driver of active galactic nuclei found at the core of some galaxies. The Milky Way galaxy is known to harbor at least one such object. Galaxies have been historically categorized according to their apparent shape, usually referred to as their visual morphology. A common form is the elliptical galaxy, which has an ellipse-shaped light profile. Spiral galaxies are disk-shaped with dusty, curving arms.

Those with irregular or unusual shapes are known as irregular galaxies and typically originate from disruption by the gravitational pull of neighboring galaxies. Such interactions between nearby galaxies, which may ultimately result in a merger, sometimes induce significantly increased incidents of star formation leading to starburst galaxies. Smaller galaxies lacking a coherent structure are referred to as irregular galaxies." [Galaxy. Wikipedia] The example "Design elements - Galaxies" was created using the ConceptDraw PRO diagramming and vector drawing software extended with the Astronomy solution from the Science and Education area of ConceptDraw Solution Park. Galaxy symbols

Question: Historically categorized by their shape, what is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas dust, and some dark matter?
Answer: Galaxy